Automatic volume control



Jan. 4, 1938. L 2,104,087

AUTOMATI C VOLUME CONTROL Filed Sept. 13, 1954 70 5/6/1641 I 50U/5CE I lINVENTOR ALFRED A. Ll SELL ATTORN EY Patented Jan. 4', 1938 UNITEDSTATES PATENT OFFICE AUTOMATIC VOLUME CONTROL Application September 13,1934, Serial No. 743,788

7 Claims.

This invention relates to radio or like receivers and more particularlyto receivers of the kind embodying so-called automatic volumecontrol, 1. e. to receivers of the kind in which the amplification ofthe receiver as a whole is varied in dependence upon received signalstrength so that between reasonably Wide limits of varying receivedsignal strength the reproduced volume remains substantially unchanged.Such receivers have the advantage, inter alia, that the effects ofso-called fading are reduced to a substantial extent.

According to this invention automatic gain control in a radio or likereceiver is effected by utilizing a direct current varying in dependenceupon received signal strength to vary the saturation of an inductanceincluded in said receiver and having a ferro-magnetic core.

In one general class of embodiment in accordance with this inventionthere is provided, in at least one tuned circuit of a radio or likereceiver of the kind referred to, an inductance having a ferro-magneticcore, means actuated in dependence upon received signal strength beingprovided for varying the magnetic saturation of said core in such manneras to cause variation of the amplification of the receiver in a sense tocompensate for the variations in received signal strength causing thevariation in saturation.

The invention, though not limited thereto, is particularly applicable tosuperheterodyne receivers and the tuned circuit including the inductancehaving a ferro-magnetic core subjected to varying saturation mayadvantageously be an intermediate frequency tuned circuit or a localoscillator tuned circuit.

Fig. 1 shows a superheterodyne receiver embodying one form of theinvention,

Fig. 2 shows a modification of the invention,

Fig. 3 shows still another form of the invention.

Referring to Fig. 1 which shows one way of carrying out the invention asapplied to a superheterodyne receiver, the said receiver includes theusual high frequency valve stage, for example, a screened grid valvestage I having its grid circuit tuned and having its output circuitcoupled to a first detector or mixing valve 2 to whose input circuit isalso applied a local oscillation generated in any convenient knownmanner either, as indicated, by a separate oscillator valve 3 or by themixing valve itself.

The output from the first detector or mixing valve is coupled to anintermediate frequency amplifier consisting of one or more stages and inone or more of said intermediate frequency stages is included a. tunedcircuit the whole or part of the inductance of which is constituted byan inductance coil having a core of ferro-magnetic material. In thearrangement illustrated the plate circuit of the first detector valve 2is coupled to the grid circuit of the first or only intermediatefrequency amplifier valve 4 by a transformer 5 whose primary andsecondary windings are Wound upon a ring-shaped ferro-magnetic core asshown. The intermediate frequency amplifier is followed by a second ordemodulating detector 6 and, if desired, an audio frequency amplifier asin the usual way. On the ferro-magnetic core is also Wound a tertiarywinding 7 to which is applied a direct current substantiallyproportional to received signal strength. This direct current may beobtained in any convenient known manner customary in radio receivershaving automatic gain control; for example, as illustrated energy fromthe output circuit of valve I is fed inductively to a coil 8 which is incircuit with a metal or other rectifier or amplifier-detector 9, therectified output from which is smoothed by the choke-condensercombination IO, N and fed through the tertiary winding 1.

Preferably the ferro-magnetic core is laminated. The usual fixedcondenser is provided in association with one of the transformerwindings thereon so as to tune it to a predetermined intermediatefrequency when the core is a predetermined condition of saturation.

With the above arrangement, it will be appreciated that the saturationof the core will vary in dependence upon the currents passed through thethird winding l and therefore the inductance of the. tuned circuitincluding a winding upon said core will also vary accordingly. In thismanner, received signal strength is caused to vary the tuning of theintermediate frequency amplifier stage in question, thus causing thesaid tuning to become closer to, or further away from, the beatfrequency obtained by the combination of the local oscillator and thereceived frequencies. Incidentally, the losses in the core will varywith the saturation, more particularly when a laminated core isemployed. This is in many cases of substantial advantage for the effectobtained will not only be to alter the tuning of the circuit with whichthe iron cored inductance is associated, but also its losses, so thatthe tuning characteristic will be varied in breadth. A condition oftendesired in practice for radio receivers is that the selectivity of thereceiver shall decrease as received signal strength increases, and viceversa, and in carrying out the present invention, it is a relativelysimple matter so to arrange the elements in the circuit that apredetermined law of combined automatic gain and. selectivity control isfollowed.

Obviously the invention maybe applied in the case of a superheterodynereceiver not only to intermediate frequency amplifiers, but also, orinstead, to the local heterodyne or to a radio frequency tuned circuit.

Fig. 2 shows the way in which the invention may be applied to the localoscillator of a superheterodyne receiver. In the arrangement of Fig. 2the grid coil I4 and the anodecoil E3 of a back coupled local oscillatorvalve 12 are wound upon a ferro-magnetic core 55 upon which is alsowound a coil il in the input circuit of the first detector or mixingvalve 2 and a fourth coil it through which the gain controlling currentderived in proportion to received signal strength is passed. It will beseen that with such an arrangement the frequency of the local oscillatorwill be varied in dependence upon received signal strength. 1

Fig. 3 shows an arrangement in accordance with this invention, andwherein there is provided in the screen grid circuit of a screened gridradio frequency amplifier valve 19, a choke consisting of a winding i8wound upon a core 2| of ferro-magnetic material, there being also woundupon this core a second winding 20 through which is passed directcurrent which is caused to be substantially proportional to receivedsignal strength. The choke coil I8 is connected between the screen gridand the positive terminal of the source of screen grid potential, thesaid positive terminal being connected to the cathode point through abypass condenser C. It will be seen that with this arrangement theinductance of the choke in the screen grid circuit will vary withreceived strength and accordingly the desired automatic gain controleffect will be obtained.

It will be observed that it is possible to utilize the present inventionto secure adequate automatic gain control without the employment of anyspecially constructed valves, such as socalled variable mu valves.

Having now particularly described and ascertained the nature of thisinvention, and in what manner the same is to be performed, I declarethat what I claim is:

1. In a radio receiver, a resonant circuit tuned to a desired highfrequency, said circuit including a coil, a ferro-magnet-ic toroidalcore, said coil being wound on the core, a high frequency circuitcoupled to said resonant circuit and having a second coil wound on saidcore, a third coil wound on the core, and means responsive to Variationsin amplitude of the energy of said high frequency for producing auni-directional current which varies directly in value with saidamplitude, and means for passing the said current through said thirdcoil to vary the saturation of said core.

2. In a radio receiver, a resonant circuit tuned to a desired highfrequency, said circuit including a coil, a ferro-magnetic toroidalcore, said coil being wound on the core, a high frequency circuitcoupled to said resonant circuit and having a second coil wound on saidcore, a third coil wound on the core, and means responsive to variationsin amplitude of the energy of said high frequency for producing auni-directional current which varies directly in value with saidamplitude, and means for passing the said current through said thirdcoil to vary the saturation of said core, in a sense such that theinductance of the first coil will be adjusted to change the tuning ofsaid resonant circuit as said amplitude increases.

3. In a radio receiver, a resonant circuit tuned to a desired highfrequency, said circuit-including a coil a ferro-magnetic toroidal core,said coil being wound on the core, a high frequency circuit coupled tosaid resonant circuit and having a second coil wound on said core, athird coil Wound on the core, and means responsive to variations inamplitude of the energy of said high frequency for producing auni-directional current which varies directly in value with saidamplitude, and means for passing the said current through said thirdcoil tovary the saturation of said core, and said core being laminatedwhereby the losses in the core will increase as said amplitudeincreases.

4. In a radio receiver, a resonant circuit tuned to a desired highfrequency, said circuit including a coil, a ferro-magnetic core, saidcoil being wound on the core, a high frequency circuit coupled to saidresonant circuit and having a second coil wound on said core, a thirdcoil wound on the core, and means responsive to variations in amplitudeof the energy of said high frequency for producing a uni-directionalcurrent which varies directly in value with said amplitude, and meansfor passing the said current through said third coil to vary thesaturation of said core, and said resonant circuit being tuned, to afrequency differing fom the frequency of the said second circuit by adesired beat frequency.

5. In a radio receiver, a resonant circuit tuned to a desired highfrequency, said circuit including a coil, a ferro-magnetic toroidalcore, said coil being wound on the core, a high frequency circuitcoupled to said resonant circuit and having a second coil wound on saidcore, a third coil wound on the core, and means responsive to variationsin amplitude of the energy of said high frequency for producing auni-directional current which varies directly in Value with saidamplitude, and means for passing the said current through said thirdcoil to vary the saturation of said core, and said resonant circuitbeing tuned to a desired intermediate frequency of a superheterodynereceiver.

6. In a superheterodyne receiver of the type including a first detectornetwork having a tunable signal selector circuit, a local oscillatornetwork having a tunable circuit which is adjustable over a frequencyrange differing from the signal selector circuit range, an automaticvolume control arrangement which includes means for deriving fromreceived signal energy a direct current voltage whose magnitude isdependent solely on the signal carrier amplitude, and means responsiveto said direct current voltage magnitude, for automatically adjustingthe frequency of the tunable oscillator circuit in a sense to reduce thefirst detector output thereby to decrease the receiver output volume.

'7. In a superheterodyne receiver of the type including a first detectornetwork having a tunable signal selector circuit, a local oscillatornetwork having a tunable circuit which is adjustable over a frequencyrange differing from the signal selector circuit range, an automaticvolume control arrangement which includes means for deriving fromreceived signal energy a direct current voltage whose magnitude isdependent on the signal carrier amplitude, means responsive to saiddirect current voltage magnitude, for automatically adjusting thefrequency of the tunable oscillator circuit, means coupling said firstdetector network and said oscillator network, and said adjusting meansbeing constructed and arranged to adjust the magnitude of said coupling.

ALFRED AUBYN LINSELL.

